lavf: deobfuscate read_frame_internal().

Split off packet parsing into a separate function. Parse full packets at
once and store them in a queue, eliminating the need for tracking
parsing state in AVStream.

The horrible unreadable loop in read_frame_internal() now isn't weirdly
ordered and doesn't contain evil gotos, so it should be much easier to
understand.

compute_pkt_fields() now invents slightly different timestamps for two
raw vc1 tests, due to has_b_frames being set a bit later. They shouldn't
be more wrong (or right) than previous ones.

libavformat/avformat.h

@@ -639,10 +639,6 @@ typedef struct AVStream {
         int nb_decoded_frames;
     } *info;
 
-    AVPacket cur_pkt;
-    const uint8_t *cur_ptr;
-    int cur_len;
-
     int pts_wrap_bits; /**< number of bits in pts (used for wrapping control) */
 
     // Timestamp generation support:
@@ -922,9 +918,6 @@ typedef struct AVFormatContext {
     struct AVPacketList *packet_buffer;
     struct AVPacketList *packet_buffer_end;
 
-    /* av_read_frame() support */
-    AVStream *cur_st;
-
     /* av_seek_frame() support */
     int64_t data_offset; /**< offset of the first packet */
 
@@ -936,6 +929,11 @@ typedef struct AVFormatContext {
      */
     struct AVPacketList *raw_packet_buffer;
     struct AVPacketList *raw_packet_buffer_end;
+    /**
+     * Packets split by the parser get queued here.
+     */
+    struct AVPacketList *parse_queue;
+    struct AVPacketList *parse_queue_end;
     /**
      * Remaining size available for raw_packet_buffer, in bytes.
      */

libavformat/seek.c

@@ -409,13 +409,13 @@ AVParserState *ff_store_parser_state(AVFormatContext *s)
     state->fpos = avio_tell(s->pb);
 
     // copy context structures
-    state->cur_st                           = s->cur_st;
     state->packet_buffer                    = s->packet_buffer;
+    state->parse_queue                      = s->parse_queue;
     state->raw_packet_buffer                = s->raw_packet_buffer;
     state->raw_packet_buffer_remaining_size = s->raw_packet_buffer_remaining_size;
 
-    s->cur_st                               = NULL;
     s->packet_buffer                        = NULL;
+    s->parse_queue                          = NULL;
     s->raw_packet_buffer                    = NULL;
     s->raw_packet_buffer_remaining_size     = RAW_PACKET_BUFFER_SIZE;
 
@@ -429,19 +429,13 @@ AVParserState *ff_store_parser_state(AVFormatContext *s)
         ss->last_IP_pts   = st->last_IP_pts;
         ss->cur_dts       = st->cur_dts;
         ss->reference_dts = st->reference_dts;
-        ss->cur_ptr       = st->cur_ptr;
-        ss->cur_len       = st->cur_len;
         ss->probe_packets = st->probe_packets;
-        ss->cur_pkt       = st->cur_pkt;
 
         st->parser        = NULL;
         st->last_IP_pts   = AV_NOPTS_VALUE;
         st->cur_dts       = AV_NOPTS_VALUE;
         st->reference_dts = AV_NOPTS_VALUE;
-        st->cur_ptr       = NULL;
-        st->cur_len       = 0;
         st->probe_packets = MAX_PROBE_PACKETS;
-        av_init_packet(&st->cur_pkt);
     }
 
     return state;
@@ -460,8 +454,8 @@ void ff_restore_parser_state(AVFormatContext *s, AVParserState *state)
     avio_seek(s->pb, state->fpos, SEEK_SET);
 
     // copy context structures
-    s->cur_st                           = state->cur_st;
     s->packet_buffer                    = state->packet_buffer;
+    s->parse_queue                      = state->parse_queue;
     s->raw_packet_buffer                = state->raw_packet_buffer;
     s->raw_packet_buffer_remaining_size = state->raw_packet_buffer_remaining_size;
 
@@ -474,10 +468,7 @@ void ff_restore_parser_state(AVFormatContext *s, AVParserState *state)
         st->last_IP_pts   = ss->last_IP_pts;
         st->cur_dts       = ss->cur_dts;
         st->reference_dts = ss->reference_dts;
-        st->cur_ptr       = ss->cur_ptr;
-        st->cur_len       = ss->cur_len;
         st->probe_packets = ss->probe_packets;
-        st->cur_pkt       = ss->cur_pkt;
     }
 
     av_free(state->stream_states);
@@ -507,10 +498,10 @@ void ff_free_parser_state(AVFormatContext *s, AVParserState *state)
         ss = &state->stream_states[i];
         if (ss->parser)
             av_parser_close(ss->parser);
-        av_free_packet(&ss->cur_pkt);
     }
 
     free_packet_list(state->packet_buffer);
+    free_packet_list(state->parse_queue);
     free_packet_list(state->raw_packet_buffer);
 
     av_free(state->stream_states);

libavformat/seek.h

@@ -31,12 +31,9 @@
 typedef struct AVParserStreamState {
     // saved members of AVStream
     AVCodecParserContext   *parser;
-    AVPacket                cur_pkt;
     int64_t                 last_IP_pts;
     int64_t                 cur_dts;
     int64_t                 reference_dts;
-    const uint8_t          *cur_ptr;
-    int                     cur_len;
     int                     probe_packets;
 } AVParserStreamState;
 
@@ -47,8 +44,8 @@ typedef struct AVParserState {
     int64_t         fpos;                   ///< file position at the time of call
 
     // saved members of AVFormatContext
-    AVStream       *cur_st;                 ///< current stream.
     AVPacketList   *packet_buffer;          ///< packet buffer of original state
+    AVPacketList   *parse_queue;            ///< parse queue of original state
     AVPacketList   *raw_packet_buffer;      ///< raw packet buffer of original state
     int raw_packet_buffer_remaining_size;   ///< remaining space in raw_packet_buffer
 

tests/ref/fate/vc1_sa00040

 #tb 0: 1/25
 0,          0,          0,        1,    38016, 0xa6f15db5
+0,          1,          1,        1,    38016, 0xa6f15db5
 0,          2,          2,        1,    38016, 0xa6f15db5
-0,          3,          3,        1,    38016, 0xa6f15db5
 0,          4,          4,        1,    38016, 0x5c4ef0e7
 0,          5,          5,        1,    38016, 0x53a42d1d
 0,          6,          6,        1,    38016, 0x68f7d89e

tests/ref/fate/vc1_sa00050

 #tb 0: 1/25
 0,          0,          0,        1,   115200, 0xb8830eef
+0,          1,          1,        1,   115200, 0xb8830eef
 0,          2,          2,        1,   115200, 0xb8830eef
-0,          3,          3,        1,   115200, 0xb8830eef
 0,          4,          4,        1,   115200, 0x952ff5e1
 0,          5,          5,        1,   115200, 0xa4362b14
 0,          6,          6,        1,   115200, 0x32bacbe7