239 строки
6.8 KiB
Plaintext
239 строки
6.8 KiB
Plaintext
@TEMPLATE decoder_tmpl.c
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Decode With Partial Drops Example
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=========================
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ INTRODUCTION
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This is an example utility which drops a series of frames (or parts of frames),
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as specified on the command line. This is useful for observing the error
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recovery features of the codec.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ INTRODUCTION
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ EXTRA_INCLUDES
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#include <time.h>
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ EXTRA_INCLUDES
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ HELPERS
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struct parsed_header
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{
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char key_frame;
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int version;
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char show_frame;
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int first_part_size;
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};
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int next_packet(struct parsed_header* hdr, int pos, int length, int mtu)
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{
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int size = 0;
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int remaining = length - pos;
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/* Uncompressed part is 3 bytes for P frames and 10 bytes for I frames */
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int uncomp_part_size = (hdr->key_frame ? 10 : 3);
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/* number of bytes yet to send from header and the first partition */
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int remainFirst = uncomp_part_size + hdr->first_part_size - pos;
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if (remainFirst > 0)
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{
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if (remainFirst <= mtu)
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{
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size = remainFirst;
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}
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else
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{
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size = mtu;
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}
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return size;
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}
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/* second partition; just slot it up according to MTU */
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if (remaining <= mtu)
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{
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size = remaining;
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return size;
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}
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return mtu;
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}
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void throw_packets(unsigned char* frame, int* size, int loss_rate,
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int* thrown, int* kept)
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{
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unsigned char loss_frame[256*1024];
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int pkg_size = 1;
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int pos = 0;
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int loss_pos = 0;
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struct parsed_header hdr;
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unsigned int tmp;
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int mtu = 1500;
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if (*size < 3)
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{
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return;
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}
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putc('|', stdout);
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/* parse uncompressed 3 bytes */
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tmp = (frame[2] << 16) | (frame[1] << 8) | frame[0];
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hdr.key_frame = !(tmp & 0x1); /* inverse logic */
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hdr.version = (tmp >> 1) & 0x7;
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hdr.show_frame = (tmp >> 4) & 0x1;
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hdr.first_part_size = (tmp >> 5) & 0x7FFFF;
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/* don't drop key frames */
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if (hdr.key_frame)
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{
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int i;
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*kept = *size/mtu + ((*size % mtu > 0) ? 1 : 0); /* approximate */
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for (i=0; i < *kept; i++)
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putc('.', stdout);
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return;
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}
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while ((pkg_size = next_packet(&hdr, pos, *size, mtu)) > 0)
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{
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int loss_event = ((rand() + 1.0)/(RAND_MAX + 1.0) < loss_rate/100.0);
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if (*thrown == 0 && !loss_event)
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{
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memcpy(loss_frame + loss_pos, frame + pos, pkg_size);
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loss_pos += pkg_size;
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(*kept)++;
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putc('.', stdout);
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}
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else
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{
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(*thrown)++;
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putc('X', stdout);
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}
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pos += pkg_size;
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}
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memcpy(frame, loss_frame, loss_pos);
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memset(frame + loss_pos, 0, *size - loss_pos);
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*size = loss_pos;
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}
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ HELPERS
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ DEC_INIT
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/* Initialize codec */
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flags = VPX_CODEC_USE_ERROR_CONCEALMENT;
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res = vpx_codec_dec_init(&codec, interface, &dec_cfg, flags);
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if(res)
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die_codec(&codec, "Failed to initialize decoder");
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ DEC_INIT
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Usage
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-----
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This example adds a single argument to the `simple_decoder` example,
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which specifies the range or pattern of frames to drop. The parameter is
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parsed as follows:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ USAGE
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if(argc < 4 || argc > 6)
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die("Usage: %s <infile> <outfile> [-t <num threads>] <N-M|N/M|L,S>\n",
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argv[0]);
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{
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char *nptr;
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int arg_num = 3;
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if (argc == 6 && strncmp(argv[arg_num++], "-t", 2) == 0)
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dec_cfg.threads = strtol(argv[arg_num++], NULL, 0);
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n = strtol(argv[arg_num], &nptr, 0);
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mode = (*nptr == '\0' || *nptr == ',') ? 2 : (*nptr == '-') ? 1 : 0;
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m = strtol(nptr+1, NULL, 0);
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if((!n && !m) || (*nptr != '-' && *nptr != '/' &&
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*nptr != '\0' && *nptr != ','))
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die("Couldn't parse pattern %s\n", argv[3]);
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}
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seed = (m > 0) ? m : (unsigned int)time(NULL);
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srand(seed);thrown_frame = 0;
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printf("Seed: %u\n", seed);
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printf("Threads: %d\n", dec_cfg.threads);
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ USAGE
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Dropping A Range Of Frames
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--------------------------
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To drop a range of frames, specify the starting frame and the ending
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frame to drop, separated by a dash. The following command will drop
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frames 5 through 10 (base 1).
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$ ./decode_with_partial_drops in.ivf out.i420 5-10
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Dropping A Pattern Of Frames
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----------------------------
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To drop a pattern of frames, specify the number of frames to drop and
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the number of frames after which to repeat the pattern, separated by
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a forward-slash. The following command will drop 3 of 7 frames.
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Specifically, it will decode 4 frames, then drop 3 frames, and then
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repeat.
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$ ./decode_with_partial_drops in.ivf out.i420 3/7
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Dropping Random Parts Of Frames
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-------------------------------
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A third argument tuple is available to split the frame into 1500 bytes pieces
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and randomly drop pieces rather than frames. The frame will be split at
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partition boundaries where possible. The following example will seed the RNG
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with the seed 123 and drop approximately 5% of the pieces. Pieces which
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are depending on an already dropped piece will also be dropped.
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$ ./decode_with_partial_drops in.ivf out.i420 5,123
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Extra Variables
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---------------
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This example maintains the pattern passed on the command line in the
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`n`, `m`, and `is_range` variables:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ EXTRA_VARS
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int n, m, mode;
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unsigned int seed;
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int thrown=0, kept=0;
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int thrown_frame=0, kept_frame=0;
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vpx_codec_dec_cfg_t dec_cfg = {0};
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ EXTRA_VARS
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Making The Drop Decision
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------------------------
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The example decides whether to drop the frame based on the current
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frame number, immediately before decoding the frame.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PRE_DECODE
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/* Decide whether to throw parts of the frame or the whole frame
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depending on the drop mode */
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thrown_frame = 0;
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kept_frame = 0;
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switch (mode)
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{
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case 0:
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if (m - (frame_cnt-1)%m <= n)
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{
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frame_sz = 0;
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}
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break;
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case 1:
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if (frame_cnt >= n && frame_cnt <= m)
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{
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frame_sz = 0;
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}
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break;
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case 2:
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throw_packets(frame, &frame_sz, n, &thrown_frame, &kept_frame);
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break;
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default: break;
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}
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if (mode < 2)
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{
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if (frame_sz == 0)
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{
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putc('X', stdout);
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thrown_frame++;
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}
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else
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{
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putc('.', stdout);
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kept_frame++;
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}
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}
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thrown += thrown_frame;
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kept += kept_frame;
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fflush(stdout);
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PRE_DECODE
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