[FFmpeg-devel] [PATCH v2] lavf/mpeg.c: improve readability of packet identification logic
Scott Theisen
scott.the.elm at gmail.com
Fri Sep 16 21:33:02 EEST 2022
Ping. Still applies cleanly.
On 5/15/22 16:18, Scott Theisen wrote:
> switch-case over es_type and then perform a linear search over
> startcode.
> ---
> This version doesn't use stdbool.h but is otherwise identical.
>
> libavformat/mpeg.c | 213 +++++++++++++++++++++++++++------------------
> 1 file changed, 130 insertions(+), 83 deletions(-)
>
> diff --git a/libavformat/mpeg.c b/libavformat/mpeg.c
> index 864b08d8f8..dfa6852453 100644
> --- a/libavformat/mpeg.c
> +++ b/libavformat/mpeg.c
> @@ -483,6 +483,7 @@ static int mpegps_read_packet(AVFormatContext *s,
> AVStream *st;
> FFStream *sti;
> int len, startcode, i, es_type, ret;
> + int identified = 0;
> int pcm_dvd = 0;
> int request_probe= 0;
> enum AVCodecID codec_id = AV_CODEC_ID_NONE;
> @@ -523,92 +524,138 @@ redo:
> goto found;
> }
>
> + // identify packet encoding
> + identified = 1;
> es_type = m->psm_es_type[startcode & 0xff];
> - if (es_type == STREAM_TYPE_VIDEO_MPEG1) {
> - codec_id = AV_CODEC_ID_MPEG2VIDEO;
> - type = AVMEDIA_TYPE_VIDEO;
> - } else if (es_type == STREAM_TYPE_VIDEO_MPEG2) {
> - codec_id = AV_CODEC_ID_MPEG2VIDEO;
> - type = AVMEDIA_TYPE_VIDEO;
> - } else if (es_type == STREAM_TYPE_AUDIO_MPEG1 ||
> - es_type == STREAM_TYPE_AUDIO_MPEG2) {
> - codec_id = AV_CODEC_ID_MP3;
> - type = AVMEDIA_TYPE_AUDIO;
> - } else if (es_type == STREAM_TYPE_AUDIO_AAC) {
> - codec_id = AV_CODEC_ID_AAC;
> - type = AVMEDIA_TYPE_AUDIO;
> - } else if (es_type == STREAM_TYPE_VIDEO_MPEG4) {
> - codec_id = AV_CODEC_ID_MPEG4;
> - type = AVMEDIA_TYPE_VIDEO;
> - } else if (es_type == STREAM_TYPE_VIDEO_H264) {
> - codec_id = AV_CODEC_ID_H264;
> - type = AVMEDIA_TYPE_VIDEO;
> - } else if (es_type == STREAM_TYPE_VIDEO_HEVC) {
> - codec_id = AV_CODEC_ID_HEVC;
> - type = AVMEDIA_TYPE_VIDEO;
> - } else if (es_type == STREAM_TYPE_AUDIO_AC3) {
> - codec_id = AV_CODEC_ID_AC3;
> - type = AVMEDIA_TYPE_AUDIO;
> - } else if (m->imkh_cctv && es_type == 0x91) {
> - codec_id = AV_CODEC_ID_PCM_MULAW;
> - type = AVMEDIA_TYPE_AUDIO;
> - } else if (startcode >= 0x1e0 && startcode <= 0x1ef) {
> - static const unsigned char avs_seqh[4] = { 0, 0, 1, 0xb0 };
> - unsigned char buf[8];
> -
> - avio_read(s->pb, buf, 8);
> - avio_seek(s->pb, -8, SEEK_CUR);
> - if (!memcmp(buf, avs_seqh, 4) && (buf[6] != 0 || buf[7] != 1))
> - codec_id = AV_CODEC_ID_CAVS;
> - else
> - request_probe= 1;
> - type = AVMEDIA_TYPE_VIDEO;
> - } else if (startcode == PRIVATE_STREAM_2) {
> - type = AVMEDIA_TYPE_DATA;
> - codec_id = AV_CODEC_ID_DVD_NAV;
> - } else if (startcode >= 0x1c0 && startcode <= 0x1df) {
> - type = AVMEDIA_TYPE_AUDIO;
> - if (m->sofdec > 0) {
> - codec_id = AV_CODEC_ID_ADPCM_ADX;
> - // Auto-detect AC-3
> - request_probe = 50;
> - } else if (m->imkh_cctv && startcode == 0x1c0 && len > 80) {
> - codec_id = AV_CODEC_ID_PCM_ALAW;
> - request_probe = 50;
> - } else {
> - codec_id = AV_CODEC_ID_MP2;
> - if (m->imkh_cctv)
> - request_probe = 25;
> + switch (es_type) {
> + case STREAM_TYPE_VIDEO_MPEG1: // 0x01
> + case STREAM_TYPE_VIDEO_MPEG2: // 0x02
> + codec_id = AV_CODEC_ID_MPEG2VIDEO;
> + type = AVMEDIA_TYPE_VIDEO;
> + break;
> + case STREAM_TYPE_VIDEO_MPEG4: // 0x10
> + codec_id = AV_CODEC_ID_MPEG4;
> + type = AVMEDIA_TYPE_VIDEO;
> + break;
> + case STREAM_TYPE_VIDEO_H264: // 0x1B
> + codec_id = AV_CODEC_ID_H264;
> + type = AVMEDIA_TYPE_VIDEO;
> + break;
> + case STREAM_TYPE_VIDEO_HEVC: // 0x24
> + codec_id = AV_CODEC_ID_HEVC;
> + type = AVMEDIA_TYPE_VIDEO;
> + break;
> + case STREAM_TYPE_AUDIO_MPEG1: // 0x03
> + case STREAM_TYPE_AUDIO_MPEG2: // 0x04
> + codec_id = AV_CODEC_ID_MP3;
> + type = AVMEDIA_TYPE_AUDIO;
> + break;
> + case STREAM_TYPE_AUDIO_AAC: // 0x0F
> + codec_id = AV_CODEC_ID_AAC;
> + type = AVMEDIA_TYPE_AUDIO;
> + break;
> + case STREAM_TYPE_AUDIO_AC3: // 0x81
> + codec_id = AV_CODEC_ID_AC3;
> + type = AVMEDIA_TYPE_AUDIO;
> + break;
> + default:
> + if (m->imkh_cctv && es_type == 0x91) {
> + codec_id = AV_CODEC_ID_PCM_MULAW;
> + type = AVMEDIA_TYPE_AUDIO;
> + break;
> + }
> + identified = 0;
> + break;
> + }
> + if (!identified) {
> + identified = 1;
> + if (startcode < 0x20) {
> + identified = 0;
> }
> - } else if (startcode >= 0x80 && startcode <= 0x87) {
> - type = AVMEDIA_TYPE_AUDIO;
> - codec_id = AV_CODEC_ID_AC3;
> - } else if ((startcode >= 0x88 && startcode <= 0x8f) ||
> - (startcode >= 0x98 && startcode <= 0x9f)) {
> - /* 0x90 - 0x97 is reserved for SDDS in DVD specs */
> - type = AVMEDIA_TYPE_AUDIO;
> - codec_id = AV_CODEC_ID_DTS;
> - } else if (startcode >= 0xa0 && startcode <= 0xaf) {
> - type = AVMEDIA_TYPE_AUDIO;
> - if (!pcm_dvd) {
> - codec_id = AV_CODEC_ID_MLP;
> - } else {
> - codec_id = AV_CODEC_ID_PCM_DVD;
> + else if (startcode <= 0x3F) { // 0x20 to 0x3F
> + type = AVMEDIA_TYPE_SUBTITLE;
> + codec_id = AV_CODEC_ID_DVD_SUBTITLE;
> }
> - } else if (startcode >= 0xb0 && startcode <= 0xbf) {
> - type = AVMEDIA_TYPE_AUDIO;
> - codec_id = AV_CODEC_ID_TRUEHD;
> - } else if (startcode >= 0xc0 && startcode <= 0xcf) {
> - /* Used for both AC-3 and E-AC-3 in EVOB files */
> - type = AVMEDIA_TYPE_AUDIO;
> - codec_id = AV_CODEC_ID_AC3;
> - } else if (startcode >= 0x20 && startcode <= 0x3f) {
> - type = AVMEDIA_TYPE_SUBTITLE;
> - codec_id = AV_CODEC_ID_DVD_SUBTITLE;
> - } else if (startcode >= 0xfd55 && startcode <= 0xfd5f) {
> - type = AVMEDIA_TYPE_VIDEO;
> - codec_id = AV_CODEC_ID_VC1;
> - } else {
> + else if (startcode < 0x80) { // 0x40 to 0x7F
> + identified = 0;
> + }
> + else if (startcode <= 0x87) { // 0x80 to 0x87
> + type = AVMEDIA_TYPE_AUDIO;
> + codec_id = AV_CODEC_ID_AC3;
> + }
> + else if (startcode <= 0x8F) { // 0x88 to 0x8F (to 0x9F excluding 0x90 - 0x97)
> + type = AVMEDIA_TYPE_AUDIO;
> + codec_id = AV_CODEC_ID_DTS;
> + }
> + else if (startcode <= 0x97) { // exclude 0x90 to 0x97
> + identified = 0; // 0x90 - 0x97 is reserved for SDDS in DVD specs
> + }
> + else if (startcode <= 0x9F) { // 0x98 to 0x9F (from 0x88 excluding 0x90 - 0x97)
> + type = AVMEDIA_TYPE_AUDIO;
> + codec_id = AV_CODEC_ID_DTS;
> + }
> + else if (startcode <= 0xAF) { // 0xA0 to 0xAF
> + type = AVMEDIA_TYPE_AUDIO;
> + codec_id = (!pcm_dvd) ? AV_CODEC_ID_MLP : AV_CODEC_ID_PCM_DVD;
> + }
> + else if (startcode <= 0xBF) { // 0xB0 to 0xBF
> + type = AVMEDIA_TYPE_AUDIO;
> + codec_id = AV_CODEC_ID_TRUEHD;
> + }
> + else if (startcode <= 0xCF) { // 0xC0 to 0xCF
> + /* Used for both AC-3 and E-AC-3 in EVOB files */
> + type = AVMEDIA_TYPE_AUDIO;
> + codec_id = AV_CODEC_ID_AC3;
> + }
> + else if (startcode < 0x1BF) { // 0xD0 to 0x1BE
> + identified = 0;
> + }
> + else if (startcode == PRIVATE_STREAM_2) { // 0x1BF
> + type = AVMEDIA_TYPE_DATA;
> + codec_id = AV_CODEC_ID_DVD_NAV;
> + }
> + else if (startcode <= 0x1DF) { // 0x1C0 to 0x1DF
> + type = AVMEDIA_TYPE_AUDIO;
> + if (m->sofdec > 0) {
> + codec_id = AV_CODEC_ID_ADPCM_ADX;
> + // Auto-detect AC-3
> + request_probe = 50;
> + }
> + else if (m->imkh_cctv && startcode == 0x1c0 && len > 80) {
> + codec_id = AV_CODEC_ID_PCM_ALAW;
> + request_probe = 50;
> + }
> + else {
> + codec_id = AV_CODEC_ID_MP2;
> + if (m->imkh_cctv)
> + request_probe = 25;
> + }
> + }
> + else if (startcode <= 0x1EF) { // 0x1E0 to 0x1EF
> + static const unsigned char avs_seqh[4] = { 0, 0, 1, 0xb0 };
> + unsigned char buf[8];
> +
> + avio_read(s->pb, buf, 8);
> + avio_seek(s->pb, -8, SEEK_CUR);
> + if (!memcmp(buf, avs_seqh, 4) && (buf[6] != 0 || buf[7] != 1))
> + codec_id = AV_CODEC_ID_CAVS;
> + else
> + request_probe= 1;
> + type = AVMEDIA_TYPE_VIDEO;
> + }
> + else if (startcode < 0xFD55) { // 0x01F0 to 0xFD54
> + identified = 0;
> + }
> + else if (startcode <= 0xFD5F) { // 0xFD55 to 0xFD5F
> + type = AVMEDIA_TYPE_VIDEO;
> + codec_id = AV_CODEC_ID_VC1;
> + }
> + else {
> + identified = 0;
> + }
> + }
> +
> + if (!identified) {
> skip:
> /* skip packet */
> avio_skip(s->pb, len);
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